Gas compressor

ABSTRACT

Compression chambers adjacent to each other in the axial direction of the rotors are communicated with each other. Therefore, a volume of air flowing and leaking from the chamber on the high pressure side into the chamber on the low pressure side is increased as compared with a case of no groove. Otherwise, a volume of air leaking from the chamber on the low pressure side into the chamber on the further lower pressure side than this chamber on the low pressure side is equal to that of the case of no groove. Therefore, the pressure in the chamber on the low pressure side becomes higher than that of the case of no groove. Accordingly, as the inner compression pressure can be enhanced, a difference between the discharge pressure and the inner compression pressure can be reduced. Therefore, a pulsation noise caused by the discharge pulsation can be reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compressor for compressing gas. Thepresent invention is effective when it is applied to a screw pump.

2. Description of the Related Art

A pressure loss generated when a fluid is flowing is increased accordingto an increase in the flow rate, that is, the flow velocity. Therefore,in general, the pressure (the discharge pressure) of gas discharged froma gas compressor is increased according to an increase in the flow rate.

In the case of a displacement compressor in which gas is compressed whenthe volume of a compression chamber is reduced, the pressure of gasdischarged from the compression chamber is determined by a compressionratio, that is, the pressure of the gas discharged from the compressionchamber is determined by the ratio of the maximum volume of thecompression chamber to the minimum volume of the compression chamber andis also determined by any leakage of gas from the compression chamber,the suction pressure and so forth.

At this time, in the case of a screw type or a scroll type displacementcompressor, while the compression chamber is being moved to thedischarge port side when the rotor is rotated, the volume of thecompression chamber is gradually reduced so as to compress gas. However,when the rotating speed of the rotor is increased and the flow rate isincreased, the discharge pressure is raised as described above.Therefore, the discharge pressure becomes higher than the pressure ofgas discharged from the compression chamber. This pressure of gasdischarged from the compression chamber is referred to as an innercompression pressure in this specification, hereinafter.

When the discharge pressure becomes higher than the inner compressionpressure, gas flows from the discharge port side to the compressionchamber side at the time when the compression chamber is communicatedwith the discharge port. As a result, the discharge pressureperiodically fluctuates, and a pulsation is generated in the pressure.Accordingly, pulsation noise is generated.

In order to solve the above problems, it is conventional to take thefollowing countermeasures. A bypass passage to communicate thecompression chamber in the middle of compression, that is, a bypasspassage to communicate the compression chamber, before the communicationwith the discharge port, with the discharge port is provided. When apulsation flow, the phase of which is shifted from the phase of apulsation flow generated on the discharge port side, is introduced intothe discharge port, the two pulsation flows, the phases of which areshifted from each other, are made to collide with each other so as toreduce the pulsation of pressure.

However, according to the above invention, the pulsation of pressure canbe reduced in a portion where the two pulsation flows, the phases ofwhich are shifted from each other, collide with each other, that is, thepulsation of pressure can be reduced in the neighborhood of a portion ofthe discharge port where the bypass passage is open. However, in otherportions, it is impossible to sufficiently reduce the pulsation ofpressure. Therefore, noise generated by the pulsation of pressure cannot be sufficiently decreased.

In this connection, in order to reduce the noise caused by the pulsationof pressure, it is necessary to enhance the rigidity of a portion in theneighborhood of the discharge port of a gas compressor so as to preventthe gas compressor from vibrating together with the pulsation ofpressure. However, this means is disadvantageous in that themanufacturing cost of the gas compressor is raised.

SUMMARY OF THE INVENTION

In view of the above points, it is a first object of the presentinvention to provide a novel gas compressor, the structure of which isdifferent from the structure of the conventional gas compressor. It is asecond object of the present invention to reduce a pulsation of pressureby reducing a difference between the inner compression pressure and thedischarge pressure.

In order to accomplish the above object, according to a first aspect ofthe present invention, there is provided a gas compressor having acompressing mechanism (1, 2) for compressing gas by operating movablemembers (1, 2) in a housing (7), comprising: a communicating passage(41) for communicating between a plurality of compression chambers (10a, 10 b) formed by the housing (7) and the movable members (1, 2).

Due to the foregoing, a volume of gas leaking from the high pressureside compression chamber (10 b) into the low pressure side compressionchamber (10 a) is increased as compared with a case in which thecommunication passage (41) is not provided.

On the other hand, a volume of gas leaking from the low pressure sidecompression chamber (10 a) to the lower pressure side compressionchamber (10 c), the pressure of which is much lower than the pressure ofthe low pressure side compression chamber (10 a), is the same as avolume of gas in the case where the communicating passage (41) is notprovided. Therefore, the pressure in the low pressure side compressionchamber (10 a) becomes higher than that of the case where thecommunicating passage (41) is not provided.

Accordingly, as the inner compression pressure can be increased, adifference between the discharge pressure and the inner compressionpressure can be reduced as compared with the conventional case.Accordingly, the pulsation noise caused by the pulsation of dischargepressure can be reduced.

Accordingly, as the necessity of enhancing the rigidity of a portion inthe neighborhood of the discharge port of a gas compressor so as toprevent the gas compressor from vibrating together with the pulsation ofpressure is low, it is possible to suppress a rise in the manufacturingcost of the gas compressor.

According to a second aspect of the present invention, the compressormechanism is a screw type compressing mechanism including a pair ofscrew-shaped rotors (1, 2), which are meshed with each other, providedas the movable members.

According to a third aspect of the present invention, the communicatingpassage is composed when a groove portion (41) is formed on an innercircumferential face, which is formed in the housing (7), facing themovable members (1, 2).

Due to the foregoing, in the screw type compressor mechanism, an innercircumferential face of the housing (7) facing the movable member (1, 2)can be easily machined. Therefore, the communicating passage (41) can beeasily formed.

According to a fourth aspect of the present invention, the grooveportion (41) is provided on a circumferential curved face (7 a) on theinner circumferential face of the housing (7).

Due to the foregoing, the load of machining the groove portion (41)composing the communicating passage can be minimized. Accordingly, adeterioration of the rigidity of the housing (7) can be minimized.

Accordingly, factors of generating the noise caused by the deteriorationof the rigidity of the housing (7) can be suppressed, that is, anincrease in the vibration and an increase in the sound emitted from theinside can be suppressed.

According to a fifth aspect of the present invention, a cross sectionalshape of the communicating passage (41) is substantially triangular.

Due to the foregoing, the communicating passage (41) can be easilyformed by means of cutting such as milling or by means of casting suchas die-casting.

According to a sixth aspect of the present invention, the groove portion(41) composing the communicating passage extends substantially inparallel with the axial direction of the movable members (1, 2).

Due to the foregoing, the groove portion (41), the cross sectional areaof which is constant, can be easily formed by means of cutting such asmilling. Accordingly, it is possible to obtain the groove (41) capableof exhibiting the same effect as that of the groove obtained bynumerical simulation. Therefore, the time necessary for designing anddeveloping the gas compressor can be reduced.

According to a seventh aspect of the present invention, the grooveportion (41) composing the communicating passage is formed at a positionon an inner wall opposing to a suction port (35) provided on the innerwall of the housing (7).

Due to the foregoing, cutting such as milling for forming the grooveportion (41) can be easily conducted from the suction port (35).

According to an eighth aspect of the present invention, a length in theaxial direction of the groove portion (41) composing the communicatingpassage is not more than a pitch size of the rotors (1, 2) composing themovable member.

Due to the foregoing, the compression chambers (10 a, 10 b) adjacent toeach other can be communicated with each other. Therefore, the innercompression pressure can be easily increased, and the pulsation noisecaused by the discharge pulsation can be reduced.

According to a ninth aspect of the present invention, the communicatingpassage (41) communicates between the adjoining compression chambers (10a, 10 b).

Due to the foregoing, the inner compression pressure can be easilyincreased, and the pulsation noise caused by the discharge pulsation canbe reduced.

Incidentally, the reference numerals in parentheses, to denote the abovemeans, are intended to show the relationship of the specific means whichwill be described later in an embodiment of the invention.

The present invention may be more fully understood from the descriptionof preferred embodiments of the invention set forth below, together withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1 is a sectional view taken in the axial direction of the gascompressor of the first embodiment of the present invention;

FIG. 2 is a perspective view showing a pair of rotors of the gascompressor of the first embodiment of the present invention;

FIG. 3 is a sectional view taken on line A-A of the housing 7 shown inFIG. 1;

FIG. 4 is a sectional view taken in the axial direction of the gascompressor of the second embodiment of the present invention; and

FIG. 5 is a sectional view taken on line A-A in FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

First, the first embodiment of the present invention will be explainedbelow. In this embodiment, the gas compressor of the present inventionis applied to a supercharger in which the combustion air supplied to aninternal combustion engine is pressurized.

In this connection, FIGS. 1 to 3 are views showing the gas compressor ofthe present invention. FIG. 1 is a sectional view of the gas compressor,FIG. 2 is a perspective view of a pair of rotors, and FIG. 3 is asectional view taken on line A-A of the housing 7 shown in FIG. 1.

As shown in FIG. 1, the gas compressor of the present embodiment is ascrew type pump including: a screw-shaped male rotor 1 and ascrew-shaped female rotor 2 (shown in FIG. 2) which are meshed with eachother; a rotation transmission mechanism 3 for driving the pair ofrotors 1, 2; and a casing 4 for accommodating the pair of rotors 1, 2and the rotation transmission mechanism 3 under the condition that thepair of rotors 1, 2 and the rotation transmission mechanism 3 areisolated form each other.

In this connection, as shown in FIG. 2, the male rotor 1 and the femalerotor 2 respectively have a male-screw-shape in which a spiralprotrusion is formed. As shown in FIG. 1, the rotation transmissionmechanism 3 is driven by a drive source such as an electric motor 50 soas to drive the pair of rotors 1, 2.

The casing 4 is comprised of three parts, which are a lubrication box 6,a rotor housing 7 and a cover 8 arranged in this order. The lubricationbox 6, the rotor housing 7 and the cover 8 are strongly joined to eachother by a joining means such as bolts (not shown).

In the lubricating oil space 9 formed in the lubrication box 6, therotation transmission mechanism 3 and the lubricant (for example, oilhaving the same viscosity as that of engine oil) supplied to therotation transmission mechanism 3 are accommodated. Gears composing therotation transmission mechanism 3 are lubricated when the lubricantaccommodated in the lubricant space 9 splashes.

A pair of rotors 1, 2 are accommodated in the rotor chamber 10 formed inthe rotor housing 7. When the pair of rotors 1, 2 are rotated in therotor chamber 10, the compression chamber 10 a formed by the rotorchamber 10 and the pair of rotors 1, 2 is successively reduced, so thatthe sucked combustion air (suction air) can be pressurized andcompressed.

The lubrication box 6 supports the input shaft 5, which is driven by themotor 50, through the first bearing 11 arranged on the motor 50 side andthe second bearing 12 arranged on the lubricant space 9 side. Inside theinsertion hole, which is formed in the lubrication box 6, into which theinput shaft 5 is inserted, the first oil seal 13 is provided in order toprevent the lubricant, which is supplied to the first bearing 11 and thesecond bearing 12, from leaking outside the casing 4.

One end side of the male rotor rotary shaft 14 is pivotally supported bythe rotor housing 7 through the third bearing 15, and the other end sideof the male rotor rotary shaft 14 is pivotally supported by the cover 8through the fourth bearing 16.

To the bulkhead for partitioning the rotor housing 7 into the lubricantspace 9 and the rotor chamber 10, the second oil seal 18 is attached inorder to prevent the lubricant, which is supplied to the third bearing15, from leaking out from the insertion hole, into which the male rotorrotary shaft 14 is inserted into the rotor chamber 10.

Into the insertion hole, which is formed on the cover 8, into which themale rotor rotary shaft 14 is inserted, the third oil seal 19 isattached in order to prevent the grease, which is enclosed in the fourthbearing 16, from leaking out into the rotor chamber 10.

In the same manner as that of the above male rotor rotary shaft 14, oneend side of the female rotor rotary shaft 20 is pivotally supported bythe rotor housing 7 through the fifth bearing 21, and the other end sideof the female rotor rotary shaft 20 is pivotally supported by the cover8 through the sixth bearing 22.

To the bulkhead for partitioning the rotor housing 7 into the lubricantspace 9 and the rotor chamber 10, the fourth oil seal 23 is attached inorder to prevent the lubricant, which is supplied to the fifth bearing21, from leaking out from the insertion hole, into which the femalerotor rotary shaft 20 is inserted, into the rotor chamber 10.

Into the insertion hole, which is formed on the cover 8, into which thefemale rotor rotary shaft 20 is inserted, the fifth oil seal 24 isattached in order to prevent the grease, which is enclosed in the sixthbearing 22, from leaking out into the rotor chamber 10.

In this connection, the rotation transmission mechanism 3 transmits arotation of the input shaft 5 to the male rotor rotary shaft 14 and thefemale rotor rotary shaft 20 so that the pair of rotors 1, 2 can besynchronously rotated. The rotation transmission mechanism 3 includes: afirst gear 31 and a second gear 32 for transmitting a rotation of theinput shaft 5, which is driven by the motor 50, to the male rotor rotaryshaft 14; and a third gear 33 and a fourth gear 34 for transmitting arotation, which has been transmitted from the second gear 32 to the malerotor rotary shaft 14, to the female rotor rotary shaft 20.

In this connection, the third gear 33 and the fourth gear 34 are timinggears for synchronously rotating a pair of rotors 1, 2.

On the inner circumferential face of the rotor housing 7, on the arcuatecircumferential curved face 7 a facing spiral protruding portions of thepair of rotors 1, 2, as shown in FIG. 3, the groove 41 extending in thedirection parallel with the axial direction of the pair of rotors 1, 2is provided. In this embodiment, a communication passage forcommunicating between the compression chambers 10 a is composed of thisgroove 41.

In this embodiment, the size L of a portion of the groove 41 parallelwith the axial direction of the rotor 1, 2 is determined to be apredetermined size not more than screw pitch p (shown in FIG. 2) of therotor 1, 2. Therefore, the groove 41 of this embodiment, that is, thecommunication passage of this embodiment can communicate between thecompression chambers 10 a, 10 b which are adjacent to each other.

In this embodiment, the groove 41 is formed by means of cutting on aface of the circumferential curved face of the rotor housing 7 opposedto the suction port 35. The cross sectional shape of the groove 41 issubstantially triangular.

Next, an outline of the operation of the compression mechanism of thepresent embodiment comprised of a pair of rotors 1, 2 will be describedbelow.

As described before, shapes of the pair of rotors 1, 2 are like malescrews in which spiral protruding portions are formed. When the pair ofrotors 1, 2 are synchronously rotated via the rotation transmissionmechanism 3, combustion air is sucked into the compression chamber 10 afrom the suction port 35 provided in the end portion of the rotorhousing 7 in the axial direction on the cover side 8.

A volume of the compression chamber 10 a is reduced while thecompression chamber 10 a is moving from the cover 8 side to thelubricant space side 9 together with the rotation of the pair of rotors1, 2. Therefore, combustion air sucked into the compression chamber 10 ais moved onto the lubricant space 9 side while the combustion air isbeing gradually compressed.

When a rotary angle of the pair of rotors 1, 2 reaches a predeterminedvalue, the compression chamber 10 a reaches the discharge port 36provided on the lubricant space 9 side, and the compression chamber 10a, which has been tightly closed up until now, is open to the dischargeport 36. Accordingly, the compressed combustion air can be dischargedfrom the discharge port 36.

In this connection, in the present embodiment, the tightly closedproperty of the compression chamber 10 a, which is formed on theopposite side to the suction port 35 with respect to the pair of rotors1, 2, is made to be higher than the tightly closed property of thecompression chamber 10 a formed on the suction port 35 side, so that thecombustion air can be mainly compressed in the compression chamber 10 aformed on the opposite side to the suction port 35 with respect to thepair of rotors 1, 2. Therefore, the discharge port 36 is provided at adiagonal position to the suction port 35 of the rotor housing 7.However, of course, the present invention is not limited to the abovespecific embodiment.

Next, the operational effects of the gas compressor of the presentembodiment will be described below.

As described above, the compression chamber 10 a is moved from thesuction port 35 side to the discharge port 36 side while the volume ofthe compression chamber 10 a is being reduced. Therefore, when thecompression chambers 10 a, 10 b, which are adjacent to each other in theaxial direction of the rotor 1, 2, are communicated with each other, thehigh pressure side compression chamber 10 b is communicated with the lowpressure side compression chamber 10 a.

Accordingly, in the present embodiment, a volume of the combustion airflowing from the high pressure side compression chamber 10 b into thelow pressure side compression chamber 10 a by leakage is increased ascompared with a case in which the groove 41 not provided. On the otherhand, a volume of the combustion air leaking out from the low pressureside compression chamber 10 a into the further lower pressure sidecompression chamber 10 c is the same as that of the case in which thegroove 41 is not provided. Therefore, pressure in the low pressure sidecompression chamber 10 a becomes higher than that of the case in whichthe groove 41 not provided.

Accordingly, as the inner compression pressure can be increased, it ispossible to reduce a difference in pressure between the dischargepressure and the inner compression pressure. Therefore, a pulsationnoise caused by the discharge pulsation can be reduced.

Since noise caused by the pulsation can be reduced, the necessity forpreventing the gas compressor from vibrating together with the pulsationby enhancing the rigidity of the neighborhood of the discharge port 36of the gas compressor is low. Therefore, it is possible to suppress anincrease in the manufacturing cost of the gas compressor.

As the cross section of the groove 41 is substantially triangular, thegroove 41 can be easily formed by means of cutting such as milling.

As the groove 41 is provided on a face of the circumferential curvedface of the rotor housing 7 opposed to the suction port 35, cutting suchas milling can be easily conducted from the suction port 35.

In this connection, in the present embodiment, the groove 41 is formedby means of cutting such as milling. However, the means for forming thegroove 41 is not limited to the above specific embodiment. When therotor housing 7 is manufactured by means of casting or die-casting, thegroove 41 may be simultaneously formed.

Even in this case in which the rotor housing 7 is manufactured by meansof casting or die-casting, when the cross section of the groove 41 issubstantially triangular, a draft taper can be easily ensured in theprocess of casting. Accordingly, the time necessary for manufacturingthe rotor housing 7 can be reduced in the same manner as that of themeans of cutting such as milling.

Next, the second embodiment will be explained below. FIGS. 4 and 5 areviews showing the second embodiment of the present invention. FIG. 4 isa sectional view of the gas compressor, and FIG. 5 is a sectional viewtaken on line A-A in FIG. 4. Referring to FIGS. 4 and 5, the secondembodiment will be explained while the points of difference from thefirst embodiment are emphasized.

In this embodiment, the groove, which composes a communication passage,is formed into a conical hollow portion 41. In this connection, themaximum diameter of the hollow portion 41 is not more than the size ofscrew pitch p of the rotor 1, 2.

Due to the foregoing, the time necessary for machining the hollowportion 41, which composes a communication passage, can be reduced.

In this connection, in FIGS. 4 and 5, like reference characters are usedto indicate like parts in the first and the second embodiment.Therefore, the explanations are omitted in this embodiment.

Finally, another embodiment will be explained below. In the aboveembodiment, the adjoining compression chambers 10 a, 10 b arecommunicated with each other, however, it should be noted that thepresent invention is not limited to the above specific embodiment.

In the above embodiment, the communicating passage is comprised of thegroove 41 or the hollow portion 41 formed on the inner circumference ofthe rotor housing 7. However, it should be noted that the presentinvention is not limited to the above specific embodiment.

In the above embodiment, the present invention is applied to a gascompressor for compressing the combustion air. However, it should benoted that the present invention is not limited to the above specificembodiment. For example, the present invention may be applied to a gascompressor for compressing other gas such as hydrogen gas.

A position at which the groove 41 or the hollow portion 41 composing acommunication passage is formed and a size of the groove 41 or thehollow portion 41 are not limited to the above specific embodiment. Theposition at which the groove 41 or the hollow portion 41 composing acommunication passage is formed and the size of the groove 41 or thehollow portion 41 are appropriately selected according to a volume ofthe leakage between the adjoining compression chambers 10 a, 10 b, thatis, according to a gap between the rotor 1, 2 and the inner wall of therotor housing 7, a compression ratio, a rotating speed (leakage length),a pressure loss of the discharge section and a machining accuracy ofeach part.

In the above embodiment, the present invention is applied to a screwtype gas compressor. However, it should be noted that the presentinvention is not limited to the above specific embodiment. For example,the present invention can be also applied to a Roots type or a scrolltype displacement compressor. As long as it agrees with the pointsdescribed in claims of the present invention, any embodiment is includedin the present invention. It should be noted that the present inventionis not limited to the above specific embodiment.

While the invention has been described by reference to specificembodiments for purposes of illustration, it should be apparent thatnumerous modifications could be made thereto by those skilled in the artwithout departing from the basic concept and scope of the invention.

1. A gas compressor having a compressing mechanism (1, 2) forcompressing gas by operating movable members (1, 2) in a housing (7),comprising: a communicating passage (41) for communicating between aplurality of compression chambers (10 a, 10 b) formed by the housing (7)and the movable members (1, 2).
 2. A gas compressor according to claim1, wherein the compressor mechanism is a screw type compressingmechanism including a pair of screw-shaped rotors (1, 2), which aremeshed with each other, provided as the movable members.
 3. A gascompressor according to claim 2, wherein the communicating passage iscomposed when a groove portion (41) is formed on an innercircumferential face, which is formed in the housing (7), facing themovable members (1, 2).
 4. A gas compressor according to claim 3,wherein the groove portion (41) is provided on a circumferential curvedface (7 a) on the inner circumferential face of the housing (7).
 5. Agas compressor according to claim 3, wherein a cross sectional shape ofthe communicating passage (41) is substantially triangular.
 6. A gascompressor according to claim 3, wherein the groove portion (41)composing the communicating passage extends substantially in parallelwith the axial direction of the movable members (1, 2).
 7. A gascompressor according to claim 3, wherein the groove portion (41)composing the communicating passage is formed at a position on an innerwall opposing to a suction port (35) provided on the inner wall of thehousing (7).
 8. A gas compressor according to claim 3, wherein a lengthin the axial direction of the groove portion (41) composing thecommunicating passage is not more than a pitch size of the rotors (1, 2)composing the movable member.
 9. A gas compressor according to claim 3,wherein the communicating passage (41) communicates between theadjoining compression chambers (10 a, 10 b).